One of the clearest criteria for Great-Book-ness is whether the ending is right. The perfect ending is, paradoxically, surprising yet inevitable: you don't see it coming until the last moment, but when it happens, you know it's right. But the surprise is inessential; indeed, it may vary widely with the perceptiveness of the reader. The rightness is crucial. I'm not a literature buff, but the best "classic" example I can think of offhand is A Tale Of Two Cities. A good recent example is The Metaphysical Touch by Sylvia Brownrigg, which was a mediocre novel overall but was salvaged because its ending was right.

The best example of a novel with the wrong ending is Le Guin's The Left Hand Of Darkness. The first two-thirds of that book were magnificent, as good as anything I've ever read; but the ending was utterly wrong: they should have died out on the ice, and Le Guin should have written a sequel about the second Mobile. Lord Of The Rings also ends wrong: Frodo and Gollum should have fallen together, while wrestling. In both cases, the author ought to have known better but wasn't willing to kill off her or his protagonist. That's understandable, but in both cases, otherwise excellent novels suffer for their authors' marketability concerns. The reader is left to imagine what should have happened--not an onerous chore, by any means, but too active an effort to maintain the proper suspension of disbelief. I suppose that--suspension of disbelief--is what it comes down to: the wrong ending makes the whole fiction seem wrong. One can still learn something from a failed fiction, of course, but it's still disappointing: not as good as it could have, should have, been.

Which me brings me to the nominal topic of this post: Neal Stephenson's The Diamond Age. It's a good book: a rich setting (too rich to summarize here) and even stronger themes, such as morality, education, and (fundamentally) the meaning of humanity. But the ending is wrong. Unlike Left Hand Of Darkness or LotR, I have no idea what the right ending would have been--in fact I suspect that none was possible given the premises (there's some authorial prestidigitation that comes back to haunt). I'm not even clear about what happened--there's too little denouement. Important questions are left unanswered. Should there be room for the reader to draw his or her own conclusions?--of course. But not too much room. For that reason, The Diamond Age, though well worth reading, is a deeply unsatisfying book.